Method of making shaped articles of an acrylonitrile polymer



Patented Dec. 16, 1952 METHOD OF MAKING SHAPED ARTICLES OF ANACRYLONITRILE POLYMER Howard M. Hoxie, Chester, Pa., assignor toAmerican Viscose Corporation, Wilmington, Del., a

corporation of Delaware No Drawing. Application October 27, 1949, SerialNo. 123,994

Claims. 1

This invention relates to the production of shaped articles, such asfibers, yarns, and films, from acrylonitrile polymers by thewet-spinning or wet-casting process.

The acrylonitrile polymers which can be formed into shaped articles inaccordance with this invention include polyacrylonitrile andfiberforming copolymers or interpolymers of acrylonitrile containing atleast 70%, preferably from 70 to 98%, of acrylonitrile in the polymermolecule and obtained by copolymerizing acrylonitrile with one or moreother polymerizable substances which contain the group C=C such asoopolymers of acrylonitrile with one or more of the following: vinylacetate, styrene, vinyl chloride, the vinylpyridines and particularly2-vinylpyridine, isobutene, dimethylfumarate, methyl methacrylate,methacrylonitrile, acrylic acid and its esters, etc.

The prior art processes for producing fibers from the acrylonitrilepolymers by the wet-spinning process involves extruding a solution ofthe polymer into a precipitant for the polymer, for example extruding asolution of the polymer in dimethylformamide into water. When thefiberforming solution is extruded into water at a practical workingtemperature C. or below), the spinning must be performed at very lowspeed and, moreover, regardless of the bath temperature, the fiberswithdrawn from the bath are so brittle and inextensible that they cannotbe stretched at ordinary temperatures, but must be stretched at elevatedtemperatures. When it is attempted to stretch these brittle,inextensible fibers by passing them through a heat-stretching tube,

considerable difiiculty is encountered in lacing the tube, and usually atube of special design is required. The brittle character and relativeinextensibility of the fibers formed in the water bath results from thefact that when the spinning solution is extruded into water it isimpossible to control the rate of diffusion of the water into theinterior of the freshly formed fibers in relation to the rate ofdiffusion of the spinning solvent out of the freshly formed fibers. As aconsequence, the fibers are set while the molecules are arranged in theheterogeneous, non-oriented condition in which they occur in the freshlyformed fibers in the setting medium. The fibers which are set in thiscondition are very weak and cannot be subjected to mechanical stress orpressure under ordinary-conditions. As pointed out above, the fiberscannot be given a godet stretch at ordinary temperature for improvingtheir handling properties and conditioning them 2 for subsequent strongstretching at elevated temperatures.

I have found that when a homogeneous mixture of the polymer anddimethylacetamide is extruded into a, setting medium comprising amixture of water and dimethylacetamide containing dimethylacetamide in acontrolled selected proportion between 20 and by volume, the fiberswithdrawn from the bath are tough and extensible and can be subjected tostrong stretching, either at ordinary temperature or at elevatedtemperature, without rupture.

The fibers advancing from the setting bath may be stretched betweengodets, as they are advanced over a thread-advancing, threadstretchingreel, or by passage through a steam tube, the extent of stretchingdepending on the temperature. For example, the fibers may be given a,stretch between godets of from to 300%, preferably 100 to 200%, atordinary temperature or at elevated temperatures up to 100 C.

or they may be stretched more than 300%, if the stretching is performedat temperatures above 100 C. This stretch may be the only stretch towhich the fibers are subjected or, if the fibers are stretched betweengodets, they may be given an after-stretch at elevated temperature,either while they are subjected to hot air, in an atmosphere of steam,wet or dry, or while they are passed through a heated liquid which isinert to the acrylonitrile polymer. The stretching may be performed onthe freshly spun fibers advancing from the setting bath, or it may bepreceded by removal of or substantial reduction in the amount ofresidual spinning solvent, for example by washing the fibers or bysubjecting them to heat to volatilize the solvent; or the stretching maybe preceded by washing and drying of the fibers. In one preferredembodiment, the fibers are stretched between godets or the like as theyare withdrawn from the bath, washed to reduce the residual spinningsolvent carried thereby to not more than 1.5% by weight, dried in air,and afterstretched 300% at a temperature of to C. by passing themthrough a steam tube. However, the non-brittle, extensible fiberwithdrawn from the water-dimethylacetamide setting bath may be sentdirectly to a steam tube and heatstretched, which method may bepreferred when the fibers are destined to be reduced to discontinuouslengths. After such heat-stretching, the fibers may be forwarded to acutter, or collected in the form of a filamentary bundle of large totaldenier such as a tow, and converted directly from tow to top, thediscontinuous fibers being treated with a non-solvent relaxing liquid,for instance hot water, which shrinks and curls the fibers. One of theadvantages to be derived from the method of the invention, in accordancewith which the dimethylacetamide solution of the acrylonitrile polymeris spun into a setting medium comprising water and from 20 to 70% byvolume of dimethylacetamide, is that it affords a choice in the mannerin which the fibers are handled, since the fibers can be stretched athigh temperatures immediately or, as is generally preferred, they can bestretched between godets at lower temperatures, including roomvtemperature, and subsequently after-stretched at higher temperature, orthey can be stretched at the lower temperatures only, with noafter-stretch- The proportion of dimethylacetamide to water in thesetting medium is critical and is between 20 and 70% by volume.Moreover, the relative proportions of dimethylacetamide and water in thesetting medium must be maintained constant or substantially constantthroughout the spinning. If the bath consists of 20% dimethylacetamideand 80% water at the start of spinning, the concentrations ofdimethylacetamide and water are maintained at 20 and 80% respectively,throughout the entire spinning operation. If the concentration ofdimethylacetamide in the setting medium is 70% by volume, or any valuebetween 20 and 70%, at the start of operations, the dimethylacetamide ismaintained constant or substantially constant at that concentration. Theconcentration of the dimethylacetamide should not vary by more than 2%and in any event must be at least 20% by volume. The composition of thesetting medium can be controlled by periodic observation of therefractive index of the medium, and the simple expedientof adding waterto the bath, in calculated amount based on the amount ofdimethylacetamide introduced as spinning solvent, either continuously orat intervals. The exact amount of water to be added will vary and cannotbe stated in advance for all conditions of spinning. As an example, thecomposition of a, setting medium consisting initially of 33% water and67% dimethylacetamide was maintained constant by adding 0.5 liter ofwater to the bath for each liter of dimethylacetamide pumped in asspinning solution.

Another remarkable and distinguishing advantage in the present method isthat the concentration of dimethylacetamide in the setting medium,within the range 20 to 70% by volume, has a direct influence on thecharacter of the fibers obtained, which can be predetermined. When thesetting medium consists of water and an amount of dimethylacetamidebetween 20 and about 45% by volume, the fibers are opaque, dull fibersof low density which, on examination under the microscope, are found tocontain numerous bubbles or voids which reduce the transparency andluster of the fibers and materially affect the dye acceptance of thefibers. The opaque fibers containing voids which are capable ofaccepting dyes are dyed to pale, pastel shades under usual dyeingconditions. Those fibers are useful for any purpose for which fibers oflow density and'luster, and dyed to pale shades are desired. on theother hand, a concentration of dimethylacetamide in the setting bath offrom about 45% up to the upper limit of the range, 70%, by volume, 'isessential to the production of fibers which, after washing, drying,

and after-stretching under heating are dense, transparent, and free ofvoids or bubbles as determined by microscopic examination. The dense,transparent fibers which are dye acceptors can be dyed to more intense,more brilliant shades under ordinary dyeing conditions than the opaquefibers obtained when the solution is extruded into a bath containingwater and a lower proportion of dimethylacetamide in the range stated.

Homogeneous mixtures of dimethylacetamide and from 5 up to 30% or more,preferably from 8 to 30%, of the a'crylonitrile polymer can be used inpracticing the invention. The immersion length is not critical and maybe from 1 to 100 inches. Immersion distances of from to inches arepreferred. Spinning may be performed. at temperatures between 25 and 60C. These are practicable working temperatures. Higher bath temperaturesmay be used if desired.

The acrylonitrile polymers which are formed into fibers in accordancewith this invention may be either homogeneous or heterogeneous, and maybe produced by any suitable polymerization process. The polymer may bepolyacrylonitrile or a copolymer or interpolymer containing from 70 to98% acrylonitrile in the molecule.

The term fibers as used herein includes fibers, filaments, threads,yarns, and filamentary bundles generally.

Although the invention has been discussed in detail in connection withthe production of synthetic fibers, it is not limited thereto. Films,sheets, tubes, rods and other shaped articles which can be obtained byextruding a solution of the polymer into a liquid setting medium can beproduced by the present method.

The following examples are illustrative of preferred specificembodiments of the invention.

Example I A spinning solution comprising a homogeneous mixture ofdimethylacetamide and 18% by weight of a copolymer containing, in thepolymer molecule, 92% acrylonitrile and 8% 2-vinyl pyridine, by weight,was extruded through a spinneret having 44 holes each 0.00; inches indiameter into a setting medium consisting of 65% dimethylacetamide andwater by volume at a temperature of 30 C. The filaments were withdrawnfrom the bath after an immersion of 8 inches, stretched 290% as theywere passed to godets immersed in water at 83 C., and washed on thegodets. The yarn was then dried on a revolving drum heated internally bysteamat a pressure of 20 lbs/sq. in. and stretched 225% in a tubecontaining steam at a pressure of lbs/sq. in. The yarn was twisted andpermitted to shrink freely in boiling water. This yarn was dense andtransparent, and did not contain voids or small bubbles as determined bymicroscopic examination of the cross-section. It was dyed to a scarletof high intensity in a dyebath containing 2%, onthe weight of the fiber,of Wool Fast Scarlet G. Supra (C. I. 252), under usual Wool-dyeingconditions.

Example II A spinning solution comprising a homogeneous mixture ofdimethylacetamide and 18% by weight of a copolymer containing, in thepolymer molecule, 92% acrylonitrile and 3% of 2-vinyl pyridine, byweight, was extruded through a spinneret containing 44 holes each 0.004inches in diameter, into a'setting medium consisting of 35% water and65% dimethylacetamide, by volume, at a temperature of 40 C. Thefilaments were withdrawn from the bath, stretched 150% at ordinarytemperature, washed by immersion in water at 95 C., dried in air, andstretched 500% in steam at a pressure of 65 lbs/sq. in. The yarn wastwisted and collected. After relaxation by free shrinkage in boilingwater, it exhibited a tenacity of 3.1 gms/denier and an extensibility of19%. The yarn did not contain voids or bubbles and was dyed to a deepscarlet in a dyebath containing 2%, on the weight of the fiber, of WoolFast Scarlet G Supra. (0.1. 252).

Example III A spinning solution comprising 18% by weight of a copolymercontaining, in the molecule, 92% acrylonitrile and 8% 2-vinyl pyridine,by weight, in dimethylacetamide, was extruded through a spinneretcontaining 40 holes each .003 inch in diameter, into a setting mediumconsisting of 37% water and 63% dimethylacetamide, by volume, at atemperature of 68 C. The filaments were withdrawn from the bath,stretched 800% in a tube containing steam at a pressure of 45 p. s. i.and the heat-stretched oriented fibers were forwarded directly to astaple fiber cutter. The staple fibers were allowed to drop into waterat 97 C. in which they were relaxed, with accompanying shrinkage andcurling. The residual dimethylacetamide was extracted from the staplefibers by the hot water. The shrunk, curled fibers were removed from therelaxing bath and dried.

The fibers contained voids or bubbles and were dyed to a pale pink shadein a dyebath containing 2%, on the weight of the fibers, of Wool FastScarlet G Supra.

Example IV A spinning solution prepared by dissolving by weight ofpolyacrylonitrile in dimethylacetamide was extruded through a spinneretcontaining forty 0.0035-inch holes into a setting medium consisting of32% water and 68% dimethylacetamide at a temperature of 30. The yarn wasremoved from the bath after an immersion of 10 inches, stretched 200% inair, washed in water at 80 C. and collected on a spool. The yarn wasallowed to dry in air at room temperature on the spool for several daysand was then stretched 350% in a tube containing hot air at 150 C. Theyarn was lustrous, free from voids and exhibited a tenacity of 3.7gms./den.

Example V A spinning solution comprising a homogeneous mixture ofdimethylacetamide and 18% by weight of a copolymer containing, in thepolymer molecule, 90% acrylonitrile and 1 2-vinyl pyridine, by weight,was extruded through a spinneret having 44 holes each 0.004 inches indiameter into a setting medium consisting of dimethylacetamide and 75%water by volume at a temperature of C. The filaments were withdrawn fromthe bath after an immersion of 6 inches, stretched 50% between godets atordinary temperature, washed by immersion in water at 93 C., andstretched 400% in steam at a pressure of '70 lbs./sq.in. The yarn wastwisted and collected. On microscopic examination the opaque yarn wasfound to contain numerous voids or bubbles. It was dyed to a pale pinkshade in a bath containing 2%, on the weight of the yarn, of Wool FastScarlet G Conc., under usual wool-dyeing conditions.

6 Erample VI A spinning solution comprising a homogeneous mixture ofdimethylacetamide and 16 by weight of a copolymer containing, in thepolymer molecule, 92% acrylonitrile and 8% vinyl acetate, by weight, wasextruded (pump speed 12 cc./min.) through a spinneret having 40 holeseach 0.0035 inch in diameter into a setting medium consisting of 66%dimethylacetamide and 34% water, by volume, at a temperature of 35 C.The filaments were withdrawn from the bath after an immersion of 6",stretched 142% between godets at ordinary temperature, washed in waterat 0., dried on a drum heated internally by steam at a pressure of 22lbs/sq. in. The dried yarn was heat-stretched 420% in a tube containingsteam at a pressure of 50 lbs/sq. in. The yarns were dense andtransparent, and did not contain voids or small bubbles.

Example VII A homogeneous mixture of dimethylacetamide and 19% of acopolymer containing 89% acrylonitrile and 11% of vinyl-a-chloroacetatewas extruded (pump speed: 15 R. P. M.) through a spinneret having 44holes each 0.004 inch in diameter, into a setting medium comprising 65%dimethylacetamide and 35% water, by volume, at 25 C. After an immersionof 8 inches, the filaments were withdrawn, stretched 114% between godetsat ordinary temperature, washed in water at 0., dried, and heatstretched 180% in hot air (240 0.). The yarn was relaxed in boilingwater. It was dense and transparent, and did not contain voids orbubbles.

Although the invention may be practed with any one of the modificationsdescribed herein, it is obvious that other changes or modifications maybe made without departing from the nature and spirit of the invention,and the invention is not to be limited, therefore, except as defined bythe appended claims.

I claim:

1. A method of making shaped articles from an acrylonitrile polymercontaining at least 70% by weight acrylonitrile in the polymer moleculewhich comprises continuously extruding a homogeneous mixture of thepolymer and dimethylacetamide into a setting medium consistingessentially of a mixture of water and dimethylacetamide containing thedimethylacetamide in a selected concentration between 20% and 70% byvolume, the water and dimethylacetamide in the setting medium beingmaintained within 2% of the selected volumetric proportions throughoutthe extrusion, and stretching the article at a temperature which is atleast room temperature afte it is withdrawn from the bath and prior tofurther treatment thereof.

2. A method of making shaped articles from an acrylonitrile polymercontaining at least 70% by weight acrylonitrile in the polymer moleculewhich comprises continuously extruding a homo geneous mixture of thepolymer and dimethylacetamide into a setting medium consistingessentially of mixture of water and dimethylacetamide containing thedimethylacetamide in a selected concentration between 20% and 70% byvolume, the water and dimethylacetamide in the setting medium beingmaintained within 2% of the selected volumetric proportions throughoutthe extrusion, and stretching the article at a temperature between roomtemperature and C. after it is withdrawn from the bath and prior tofurther treatment thereof.

3. A method of making synthetic fibers from an acrylonitrile polymercontaining at least 70% by Weight acrylonitrile in the polymer moleculewhich comprises continuously extruding a homogeneous mixture of thepolymer and dimethylacetamide through a spinneret into a setting mediumconsisting essentially of a mixture of water and dimethylacetamidecontaining the dimethylacetamide in a selected concentration between 20%and 70% by volume, the water and dimethylaoetamide in the setting mediumbeing maintained within 2% of the selected volumetric proportionsthroughout the extrusion, withdrawing the fibers from the settingmedium, stretchingthe fibers from 100% to 300% at a temperature up to100 C. after they are withdrawn from the bath and prior to any othertreatment thereof, washing the fibers, and subsequently furtherorienting the fibers by simultaneous. heating and stretching.

4. The method of claim 3, wherein the setting medium consistsessentially of a mixture of water and dimethylacetamide containing thedimethylacet'amide in a selected concentration between 20% and about 45%by volume.

5. The method or claim 3, wherein the setting mediumconsists essentiallyof a mixture of water and dimethylacetamide containing thedimethylacetamide in a selected concentration between about 45% and 70%by volume.

6. A method as in claim 1, wherein the acrylonitrile polymer is acopolymer containing, in

the molecule, from 90 to 92% of acrylonitrile and from 8 to 10% ofZ-Vinylpyridine, by weight.

7. A method as in claim 1, wherein the acrylonitrile polymer is afiber-forming polyacrylonitrile.

8. A method as in claim 1, wherein the acrylonitrile polymer is acopolymer containing 92% acrylonitrile and 8% vinyl acetate, by weight,in the polymer molecule.

9. A method as in claim 1, wherein the acrylonitrile polymer is acopolymer containing 89% acrylonitrile and 11% vinyl-a-ohloroacetate byweight, in the polymer molecule.

10. A setting bath for use in the production of shaped articles from ahomogeneous mixture of dimethylacetamide and an acrylonitrile polymer,which bath consists essentially of a mixture of water anddimethylacetamide containing the dimethylacetamide in a selectedconcentration between 20 and by volume.

HQWARD M. HOXIE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,404,? 17 Houtz July 23, 19462,420,565 Rugeley et a1. May 13, 1947 2,531,407 DAlelio Nov. 28, 1950

1. A METHOD OF MAKING SHAPED ARTICLES FROM AN ACRYLONITRILE POLYMERCONTAINING AT LEAT 70% BY WEIGHT ACRYLONITRILE IN THE POLYMER MOLECULEWHICH COMPRISES CONTINUOUSLY EXTRUDING A HOMOGENEOUS MIXTURE OF THEPOLYMER AND DIMETHYLYACETAMIDE INTO A SETTING MEDIUM CONSISTINGESSENTIALLY OF A MIXTURE OF WATER AND DIMETHYLACETAMIDE CONTAINING THEDIMETHYLACETAMIDE IN A SELECTED CONCENTRATION BETWEEN 20% AND 70% BYVOLUME, THE WATER AND DIMETHYLACETAMIDE IN THE SETTING MEDIUM BEINGMAINTAINED WITH 2% OF THE SELECTED VOLUMETRIC PROPORTIONS THROUGHOUT THEEXTRUSION, AND STRETCHING THE ARTICLE AT A TEMPERATURE WHICH IS AT LEASTROOM TEMPERATURE AFTER IT IS WITHDRAWN FROM THE BATH AND PRIOR TOFURTHER TREATMENT THEREOF.